A molded resin product obtained by joining together two or more resin molding members by laser welding is conventionally known. Laser welding is a method of irradiating laser light on an overlapping part having overlapped therein a transmitting material which transmits laser light and an absorbing material which absorbs laser light, from the side of the transmitting material to weld together the absorbing material and the transmitting material.
Other methods for joining resin members together, means such as vibration welding, ultrasonic welding and bonding by an adhesive are known, but taking into consideration the effect on an electronic component or the like incorporated into the molded resin product, the degree of freedom in joining, airtightness thereof and the like, the technique of laser welding is excellent.
In recent years, polyphenylene sulfide (PPS) is attracting attention as a thermoplastic resin excellent in heat resistance and chemical resistance, and a technique of joining a thermoplastic resin by laser welding is disclosed in Japanese Unexamined Patent Publication Nos. 2006-205619, 2006-168221, 2006-096886, 2005-015792 and 2005-007759. These techniques consist of joining together members each comprising polyphenylene sulfide.
However, polyphenylene sulfide is expensive and therefore, polyphenylene sulfide may only be used in a site requiring heat resistance, chemical resistance or the like, and form the remaining sites from other thermoplastic resins, thereby obtaining an inexpensive molded resin product while ensuring durability. Polyphenylene sulfide also has a high melting point, but an organic dye having heat resistance close to the melting point is not found at present. Accordingly, there is a problem that when a molded resin product is produced using only members comprising polyphenylene sulfide, the product cannot be colored in a desired color and is restricted in design.
In order to solve this problem, a technique of joining together a member comprising polyphenylene sulfide and a member comprising a relatively inexpensive and colorable thermoplastic polyester having a low melting point, by laser welding is desired.
However, it is difficult to weld together two members comprising such different thermoplastic resins.
A technique for achieving laser welding of members comprising different thermoplastic resins is disclosed in Japanese Unexamined Patent Publication No. 2006-312303. In this technique, a compatibilizer being compatible with both a thermoplastic resin constituting a first resin molding and a thermoplastic resin constituting a second resin molding is mixed in the resin composition of the second resin molding.
However, there is no compatibilizer that is compatible with both polyphenylene sulfide and a thermoplastic ester, and therefore, this technique cannot be employed in joining together a member comprising polyphenylene sulfide and a member comprising a thermoplastic polyester.